Hydroelectric turbine installations in which the turbine comprises several adjustable pitch runner blades are widely used. In these turbines, each runner blade (often simply called a "blade"), is pivotally connected to the hub and rotatable about an axis extending in a direction generally perpendicular to the hub. The rotation of each blade about its axis permits the turbine operator to seek optimum efficiency of the hydroelectric installation under the entire range of operating conditions of the turbine. In the hydroelectric industry, turbines with adjustable pitch blades are commonly referred to as "Kaplan turbines". Kaplan turbines are also typically provided with adjustable wicket gates designed to regulate the flow of water admitted to the turbine. Although providing hydroelectric installations with adjustable pitch blades can materially improve the efficiency of the installations, some potential concerns result from the functional design requirements of Kaplan turbines.
One such potential concern with Kaplan turbines involves the maintenance of certain components necessary for permitting rotation of the blades such as bearings, pins, shafts, seals, bushings and other devices. Some of these components are particularly subject to severe operating conditions and may require replacement. One such component is the trunnion bushings (or bearings) used to support the blades for rotation about the horizontal axes. Replacing worn-out trunnion bushings is particularly time consuming because the runner must be removed from its operating position, disassembled and then reassembled. The disassembly includes all the rotating components and most stationary components above the runner assembly, which for a typical Kaplan turbine runner may require from 700 to 750 man hours. Further, replacing these trunnion bushings is costly due to equipment and manpower needed to remove the turbine runner from the water passageway.
Another potential concern is the inadvertent release of lubricating fluid from the hub of Kaplan turbines. More specifically, a lubricating oil (or so called hub oil) is typically provided in the runner hub for lubrication of runner blade trunnion, trunnion bushings, and other rotating or sliding parts of hub operating mechanisms. With these systems, the hub enclosure is pressurized to prevent water from leaking in through the seal part of the runner blade trunnion. While this approach effectively prevents water from entering the hub, it also increases maintenance problems and creates the risk of oil leaking and flowing out of the hub and into the water passage. If the seal packing of the runner blade trunnion or trunnion itself is damaged, defective, or worn-out, contamination of the water may result.
Accordingly, it appears desirable to develop turbine installations in which certain components of the hub allowing rotation of the blade are modified to permit replacement of worn-out components without removing the runner from its operating position (i.e., without performing a total disassembly of the hub), to reduce maintenance time and expense. In addition, it appears desirable to develop turbine installations in which the lubricating oil typically filling the hub can be replaced with an environmentally compatible fluid or non-toxic media, such as water, biodegradable oils and/or a gas such as air, so that leakage of hub fluid is not a concern.